Conventionally, DC feeder systems are known as power supply systems for a DC electric railroad. Such DC feeder systems have characteristics that a load change due to start and stop of a railroad vehicle frequently occurs, and the line voltage change is large.
It is typical that DC is produced from an AC power source system using a power converter like a diode rectifier, and power regeneration to the AC power source system at the deceleration of a railroad vehicle cannot be performed without an installation of a regenerative inverter. Hence, when no regenerative inverter is present, it is difficult to perform effective regeneration unless a sufficient load that absorbs regenerative currents from the railroad vehicle is present around the railroad vehicle.
Conversely, even if the regenerative inverter is installed, if there is no load that consumes power regenerated by the inverter in the system, the regenerative power causes a reverse power flow to the power transmission-distribution system of an electric power company, and thus it is difficult for the railway business operator to accomplish an effect of reducing the amount of power to be purchased.
In order to address such a disadvantage, an electric energy storage device that absorbs regenerative power of the vehicle is installed in the feeder system in some cases. This electric energy storage device is capable of absorbing the regenerative power of a railroad vehicle, and also capable of discharging the stored energy. The installation of the electric energy storage device enables a reduction of the input energy of the transformer station for power feeding. Moreover, some electric energy storage devices have a function of suppressing a change in a line voltage. An example prior art document for such an electric energy storage system is as follow: